The invention concerns spinal osteosynthesis systems, in particular for anterior fixation.
The document FR-2,731,344 (U.S. Pat. No. 5,938,663) discloses a spinal osteosynthesis system comprising a rod, a vertebral screw having a body to be anchored in a vertebra, and a head in the form of a threaded rod. The system comprises a connector with two branches which can be engaged on the screw head. A clamping nut can be fitted on the screw head in order to clamp the two branches between the base of the screw head and the nut. The rod engaged between the branches is thus clamped and immobilized.
This system has many advantages. As it includes a small number of components and is easy to put in place, it permits rapid fitting during a surgical intervention. However, the nut has a hexagonal outer profile which is necessary to permit its maneuvering and its clamping by means of a socket wrench. Now, such a profile generates numerous sharp edges and projecting corners capable of damaging the body tissues coming into contact with the nut. Similarly, it is difficult to prevent a threaded end part of the screw head from protruding from the nut upon completion of clamping. Now, this thread itself also presents projecting edges which can be damaging to the body.